Stagger time with swimmer (6)
I believe the answer is:
totter
'stagger' is the definition.
(I've seen this before)
'time with swimmer' is the wordplay.
'time' becomes 't'.
'with' means one lot of letters go next to another.
'swimmer' becomes 'otter' (I have seen 'Good swimmer' mean 'otter' so perhaps 'swimmer' could also mean 'otter').
't'+'otter'='TOTTER'
(Other definitions for totter that I've seen before include "Be unsteady on one's feet" , "Maybe a mathematician" , "I add" , "Waver and threaten to fall" , "Move unsteadily; be about to fall" .)